Positron tomography has reached a critical point in its development. Numerous studies have shown that this technique can produce useful information in animal and man that cannot be provided by any other imaging system. However, positron imaging has been limited because of relatively poor resolution. We have developed powerful techniques of analog coding which permits the design of high resolution instruments. PCR-I is an analog coded single ring prototype system for positron tomography. The system currently is operating at 4.5mm resolution without the use of interpolative motion. Studies are underway using phantoms and animal systems to study areas of application of this instrument. This instrument shows high resolution, high sensitivity, relatively low random and prompt scatter coincidence rates and excellent stability and linearity. Based on the design of PCR-I, we propose to develop an analog coded cylindrical positron tomograph to image volume distributions of positron emitting activity. Physical studies will be carried out using Monte Carlo calculations and experiments to determine the effects of randoms and prompt scatter coincidences. Studies will be carried out for different source geometries and activity levels. By use of a powerful simulation program, the design parameters of PCR-II, an analog coded cylindrical positron tomograph, will be determined. Again, by use of simulation, the performance of the instrument will be predicted for different imaging tasks. PCR-II will provide an instrument with resolution approaching the physical limitations of positron range and small angle deviation and yielding very high sensitivity and count rate capability. The two dimensional analog coding permits each phototube to identify a large number of detector elements, thus permitting a design with thousands of detectors. The system will also operate without interpolative motion. Stability and linearity should be equal to that of PCR-I. A three dimensional reconstruction algorithm will be used to reconstruct the source distribution within the volume source. The problems encountered in use of this algorithm will be investigated again by simulation.